The basic operation and functions of various parts of ejection apparatus are now rather well known, although there are different approaches to solving the problems. In one form of system, the canopy is eliminated, the seat and occupant are propelled out of the aircraft through the canopy opening, and a parachute is deployed to lower the occupant safely to earth. Other systems use capsules enclosing the occupant, or other techniques, but those are not of relevance here.
Various problems inherent in ejection and deployment, which are familiar to those skilled in this art, are determining the speed and altitude and, in some cases, the attitude, of the seat at the time of ejection and either measuring conditions or estimating a time after ejection at which a parachute can or must be deployed to give reasonable assurance of safety to the occupant. If the speed is too great, the parachute can be damaged when it opens or the occupant can be subjected to excessive deceleration shock, or both. These and other problems, and some of the solutions to them, are discussed in the following U.S. patents:
U.S. Pat. No. 2,505,869 Quilter, PA1 U.S. Pat. No. 2,693,326 Lobelle, PA1 U.S. Pat. No. 2,699,305 Turner et al. PA1 U.S. Pat. No. 3,067,973 Halsey et al. PA1 U.S. Pat. No. 3,311,330 Hofferberth et al. PA1 U.S. Pat. No. 3,352,518 Turner et al. PA1 U.S. Pat. No. 3,355,127 Stanley et al. PA1 U.S. Pat. No. 3,421,720 MacDonald, Jr., et al. PA1 U.S. Pat. No. 3,547,383 Carpenter, Jr. PA1 U.S. Pat. No. 3,669,388 Van Kreuningen PA1 U.S. Pat. No. 3,726,499 Stencel PA1 U.S. Pat. No. 3,862,731 McIntyre PA1 U.S. Pat. No. 4,057,206 Duncan et al.
While some of the techniques disclosed in these references can be successfully employed, certain problem areas remain, particularly in the reliability of the control equipment and in the accuracy of the airspeed determination.
The control equipment, commonly referred to as a "sequencer", involves electronic circuit apparatus, to a greater or lesser degree of complexity, depending on the design approach used. It has been found that these control circuits are subject to disturbance by electromagnetic "noise", i.e., ambient radio and radar transmissions which have no direct connection with the system. Thus, the control apparatus sometimes fails to operate properly when the aircraft is "immersed" in radio and radar signals from, for example, an aircraft carrier or the control tower of a field on which the aircraft is supposed to land.
Also, because the travel characteristics of a seat and occupant, apart from the aircraft, are difficult to predict accurately, there have been problems in determining the optimum time at which parachute deployment and seat/occupant separation should occur.